The present invention relates generally to a device for determining directional information relative to an external magnetic field. More particularly, this invention pertains to a light-reflective device for determining directional information relative to an external magnetic field.
There are no known light-reflective devices available that can be used to determine directional information relative to an external magnetic field. While there are some existing patents relating to light-transmission devices operable for determining directional information relative to an external magnetic field, none of these patents address the problems solved by the present invention. In addition, none of these patents discloses the concept of using a light-reflective device to determine directional information.
U.S. Pat. No. 4,414,754, issued to Lapeyre on Nov. 15, 1983 and entitled "High Resolution Compass Card Position Decoder," discloses a light-transmission device for determining directional information relative to an external magnetic field. The '754 device includes a disk having a light-transmission pattern, a light source on one side of the disk, and an array of light detectors on the other side of the disk. The '754 device does not disclose the use of a disk having a light-reflective pattern.
Another patent, U.S. Pat. No. 5,448,835, issued to Lewis on Sep. 12, 1995 and entitled "Compass device," discloses a light transmission device for determining directional information relative to an external magnetic field. The '835 device includes a light source, a variable-width, slotted compass card for transmitting light, a magnet, and two light detecting devices. The '835 device also does not disclose the use of light-reflective disk. The size of the magnet used in the '835 device is limited by the light-transmission compass card. Smaller magnets limit the torque available to rotate the compass card, reduce the response time of the device, and adversely affect the balance of the device. The '835 device is also sensitive to the intensity of light striking the compass card. Variations in the intensity of light passing through the compass card may generate errors in the directional information.
What is needed, then, is a device that is insensitive to variations in the intensity of light striking the compass card and includes a larger, more balanced magnet.